- Rheumatoid arthritis is a chronic inflammatory disease affecting an estimated 10 million individuals in the United States alone. Currently, no effective long-term treatment other than joint replacement surgery is available. The overall aim of this proposal is to develop an in vivo gene therapy protocol for the treatment of arthritis. The first-generation gene therapy protocol using retroviral-mediated gene transduction demonstrated that antagonists of two cytokines, interleukin-l (IL-l) and tumor necrosis factor alpha (TNFa), can provide a significant therapeutic outcome in animal models of arthritis. These results are encouraging and provide the foundation of these proposed studies; however, it will never be practical to treat the millions of Americans who suffer from arthritis using an ex vivo strategy. Ex vivo treatments require sophisticated laboratories and protocols for transduction and selection of explanted cells. The goal of these studies is to develop an in vivo protocol in which gene transduction requires nothing more than an injection into the afflicted joint and thus, could become widely available in settings as simple as a physician's office. In vivo gene delivery will be accomplished with the injection of engineered Herpes simplex virus 1 (HSV1) vectors. HSV-l vectors have the advantages of high infectivity and the potential to express multiple transgenes. The major disadvantage of HSV vectors, their cytotoxicity, has largely been overcome by the deletion of the cytotoxic genes, ICP4, ICP22, ICP27, and UL41. These multiple deletion mutants are capable of replication only in complementing cell lines. They show greatly reduced cytotoxicity both in cell culture and in rabbit synovium with the acquired capacity for durable transgene expression in vivo. By using these replication-defective vectors, the principal investigator will be able to transduce synoviocytes in vivo to express antagonists of IL-l and TNFa, setting the stage for a simple and effective gene therapy treatment for arthritis. Four specific aims are proposed: 1) To construct HSV-l gene therapy vectors with further reduced cytotoxicity by deletion of the ICP0 gene; 2) to engineer HSV-1 vectors for coordinated expression of therapeutic genes; 3) to assess the effect of prior immunization with HSV on vector persistence and expression and to determine the effect of "antigenic stealthing" genes; 4) to assess the efficacy of HSV-l vectors for the direct in vivo gene therapy of the antigen-induced rabbit model of arthritis.